1. Field of the Invention
The present application relates to a solenoid and a solenoid valve.
2. Discussion of the Background
Hydrogen tanks in fuel-cell vehicles, for example, contain hydrogen at a high pressure, such as 35 to 70 MPa. Therefore, hydrogen tanks are required to have an opening portion, to which a valve device (solenoid valve) is attached, with a small opening area. To ensure sufficient flow rate from a hydrogen tank to a fuel cell, the solenoid valve is required to have a valve disc with a large stroke. In, for example, a hydrogen tank in a fuel-cell vehicle, there is a large pressure difference across the valve disc. In such a case, a large thrust (attraction force) is required in the initial stage of operation for opening the valve disc.
Various types of solenoids have been proposed which are suitable for when the valve disc is moved at a large stroke or when there is a large pressure difference across the valve disc. For example, Japanese Patent No. 4243901 describes a solenoid including a plunger (movable body) and a core (base) having surfaces inclined with respect to the axial direction in areas where a thrust is generated. Accordingly, the surface area is increased and sufficient thrust is generated even when the stroke is large. Japanese Unexamined Patent Application Publication No. 9-199322 describes a solenoid including a plunger (movable iron piece) having a projection and a core (iron core) having a recess. The projection and the recess are positioned close to each other in the initial stage of operation (before the operation), for moving a valve disc at a large stroke. Accordingly, a large thrust can be generated. Japanese Unexamined Patent Application Publication No. 2007-173448 describes a solenoid including, in addition to the basic structure including a plunger, a core, a coil, and a casing, an additional component for generating a large thrust when the stroke is large.